[T3] Stupid question #395 Oil change time?

William Jahn willjahn975 at gmail.com
Thu May 30 11:08:30 PDT 2019

Jim good write up and it makes sense. I understand how multi grade oils
work now from calling and doing research. It all has to do with flow rates
and yes 20W50 does not become thicker as I always thought it is all about
how long it stays at the bearing do to pressure and flow rates. My only
fear is going to a SAE 30 rather than a SAE 40. Reason is SEA 40  is what I
always used and I think I hear some noise even though this engine only has
at most 35,000 miles on it and could be the result of using the 20W50
castrol which I used for the last 4 oil changes.   If I deal with autozone
they do have both in the STP brand for less than Valvoline which they only
offer in multigrade which I would prefer to say away from. I don't know if
STP is a good engine oil it's not the thick crap one would add it's just
oil. Valvoline conventional does have 860 ppm zinc. Trouble is no matter
what oil company I call or chat with I get a different answer Valvoline
told me SAE 40 does not thin out yet I know it has to . When I pour in the
20W50 it is thin and when I drain it it is thin yet it does cling pretty
well when trying to empty the drain pan yet by then it's cooled down.
Bentley does put SAE 30 and SAE 40 in the tropical range class. I need to
locate the Lucas additive somewhere my thinking is since Valvoline does
have 830 ppm that's better than none.

On Thu, May 30, 2019 at 10:06 AM Jim Adney <jadney at vwtype3.org> wrote:

> Some comments on oil. Some of these are pet peeves, so forgive me if this
> seems pedantic.
> 1) There's no such thing as 30W oil. Same for 40W, 30 w, 30w, 30 W, 40 W,
> 40w or 40 w. Likewise for 10, 20, and 50. These are properly called SAE
> 30,
> etc.
> The W stands for Winter and only appears on multi-viscosity oils, as in
> 10W-40, etc, or SAE 10W-40 to be complete.
> I note that the Tractor Supply web site makes this mistake consistently:
> Although the labels on their bottles all state SAE 30, etc, Tractor Supply
> consistently describes them as 30W or 30w. This is simply a
> misunderstanding of what the W means, and is wrong.
> It's common for people to mention 30-weight oil and this often gets
> condensed to 30W, because people see that W on the label and confuse the
> W with weight. I accept this use of "weight" even though there's little
> difference in mass and what we mean is viscosity. What we mean, and what
> we should recognize, is that we're talking about SAE 30, SAE 10W-40, etc.
> (SAE = Society of Automotive Engineers, the group that wrote the
> specification.)
> In multi-vicosity oils, the W (winter) viscosity is measured at (I
> believe) 32 F
> (0 C) while the hot viscosity is measured (I believe) at 212 F (100 C.)
> But the
> 2 measurements are made on different viscosity scales, so this can be
> misleading. A 30W-30, if such a thing existed, would not have the same
> viscosity at both 32 F and 212 F. SAE 20W-50 is thinner at 100 F than it
> is
> at 32 F, but it hasn't thinned down as much as SAE 20 would have.
> Note that this means that SAE 20W-50 does NOT get more viscous as it
> gets warm.
> I believe the viscosity scales used for gear oils are also different from
> those
> used for engine oils, and they also use different scales for hot and cold.
> So
> you'll see 80W-90 gear oils. These come in grades like GL-4 and GL-5,
> where I believe GL stands for Gear Lubricant.
> 2) I don't see any reason why you could not mix any petro engine oils
> together for some kind of intermediate outcome, but it's quite possible
> that
> mixing synthetic and petro oils might not work. I don't know about that.
> 3) I bought a 16 oz. bottle of Lucas "Racing ZDDP / TB Zinc-Plus / Engine
> Break-In Oil Additive" " #0 49807 10063 6 at my FLAPS yesterday for $13.61
> after tax. The Lucas spec sheet lists this as having 43,000 ppm of zinc,
> so I
> ran the numbers to see what this would mean for us.
> We should get 4000+ ppm additional ZDDP if we add 4 oz (1/4 bottle, $3.40)
> to one oil change (5.3 pts = 42.4 oz)
> or 2000+ ppm of additional ZDDP if I add 2 oz (1/8 bottle, $1.70) to each
> oil
> change.
> The bottle states that it is NOT recommended for any vehicle later than
> 1994
> or that requires oil meeting API (American Petroleum Institute) spec SG or
> later. "May cause damage to catalytic converters." I believe the latest
> spec
> called out for our cars was SD.
> I'm going to start using ~2 oz with each oil change. I agree with Brian
> that
> the fancy, high-priced oils are probably not worth it for us, but I think
> the
> ZDDP probably is. I would use twice as much for break-in of a new engine.
> 3) Because it gets quite cold around here, and I have engines that get
> driven
> occasionally in that cold, I think I'll continue to use the cheap Diesel
> 15W-40 year round but with the addition of the Lucas ZDDP additive. This
> is
> a cheap, effective solution for year round use in climates that see temps
> well
> below freezing. If I lived in a warm climate, I'd find SAE 30, add 2 oz of
> the
> Lucas ZDDP additive and use that year round.
> 4) It may also have been Brian who mentioned how it was more important to
> value flow to the bearings over pressure in the oil passages. I agree with
> this. The only pressure that counts is the pressure that's developed
> between
> the rotating shaft and the bearing. I'll try to explain why oil pressure
> isn't as
> important as oil volume.
> If you don't already understand this, it may be helpful to draw yourself a
> picture of a rotating circle within another circle. The rotation of the
> center
> circle drags the oil around it.
> Now draw another set of circles with the center circle a bit off-center.
> This
> creates a "wedge" where the dragged-along oil gets pushed into a tighter
> and tighter space. This is where the rotation of the center circle creates
> pressure, and that's the pressure that keeps the 2 parts from touching.
> The pressure developed depends on the speed of rotation, the viscosity of
> the oil, the width of the bearing, and how tight the wedge gets. It gets
> higher
> as the shaft gets closer to touching the bearing. If the clearance gets
> close,
> the pressure can get extremely high: much higher than the oil delivery
> pressure. This is what keeps the two parts from ever actually touching,
> and
> this is why plain journal bearings work so well.
> Note that this all depends on the oil being virtually incompressible, so
> if
> you're delivering air or foam to the bearing there will be almost no
> pressure
> developed in the wedge and the shaft is likely to rub against the bearing.
> This may happen each time we start, but there is likely to be a thin layer
> of
> oil still there to prevent actual metal to metal contact.
> Note that this explains why the oil entry points in a bearing may seem to
> be
> in odd places. The people who design engines have found that they need to
> inject oil at the low pressure areas so that the rotation of the shaft can
> put
> the most pressure where it's most needed. The worst possible place to try
> to
> inject oil would be where the wedge effect is trying to build pressure;
> that
> would just give the pressurized wedge of oil a path to escape, allowing
> the
> parts to touch.
> This may help you understand why it is not necessarily a good idea to
> choose a higher viscosity oil. The higher viscosity will make it harder to
> pump, especially during warmup, and may be slower getting to the places
> where it's needed. It takes more engine power to pump, so it will cause
> more
> wear on the pump and the parts that drive the pump. If you have a filter,
> it
> will be harder to pump thru the filter and that puts even more load on the
> pump, its drive, and the engine. While the higher viscosity will increase
> the
> wedge pressure in the bearing, that's probably not as useful as being SURE
> of plenty of flow into the bearing.
> 5) Note that in 1970 VW increased the size of the oil passages, but didn't
> change the size of the oil pump. If that was all they did, this would have
> meant the same flow, but with reduced oil delivery pressure. However, VW
> also changed the pressure relief system, so this muddies the picture. They
> didn't change the oil pressure switch, so it seems likely that the
> pressure
> relief system changed to keep the oil galley pressures pretty much the
> same.
> However, in 1972, they increased the size of the oil pump without changing
> anything else. This clearly increased flow and should have increased
> pressure, too, but we don't see the pressure increase, probably because
> the
> pressure relief valve works well and because of where we measure the
> pressure, unless we use oils with higher viscosities than VW ever
> recommended. These late engines seem to have better longevity than the
> earlier ones.
> Thanks for reading. I hope it wasn't too painful.
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
> _______________________________________________
> VWType3.Org mailing list - type3 at vwtype3.org
> To unsubscribe or change subscription options, visit:
> http://lists.vwtype3.org/listinfo.cgi/type3-vwtype3.org
> If you need more help, contact: gregm at vwtype3.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.vwtype3.org/pipermail/type3-vwtype3.org/attachments/20190530/154fd991/attachment.html>

More information about the type3-vwtype3.org mailing list